The problem of bread staling is of great economic importance to the consumer as well as to the baking industry. Since a major criteria in the selection of bread and other similar products is based on soft texture, losses due to customer rejection of breads, rolls, yeast-raised and cake doughnuts due to staling or perceived staling are extensive.
The staling of bread is perceived by a firming of the crumb and loss of pleasant aroma of freshly baked breads. Staling begins immediately after baking and continues as the bread ages. Staling is the result of retrogradation of cooked starch and visco-elastic changes in gluten after baking. Staling bread becomes firmer in texture even though the water content of packaged stale bread does not vary significantly from fresh bread.
In the United States, unsold breads are removed from the supermarket shelves a few days after delivery. These breads will stay on thrift shop shelves for a few additional days. Unsold breads are then disposed to hog farms or feed lots. A one day increase in shelf life of bread could result in large potential savings for the baker and the consumer.
Some of the measures now in commercial use to deal with the bread staling problem include the use of fungal enzymes and glycerol monoesters of long chain fatty acids such as glycerol monostearate. Fungal enzymes (proteases and amylases) are relatively inefficient antistaling agents because these enzymes have relatively low inactivation temperatures (below about 65.degree. C.). Most of the enzyme activity is lost in the early stages of baking. Glycerol monostearate, when added to dough, results in softer bread. However, the bread continues to stale at the same rate after baking. The increased initial softness gives the impression of antistaling.
Amylolytic enzyme additives are presently used in bakery goods to supplement amylolytic enzyme deficiencies in flour to increase gas production. Proteolytic enzymes are added to reduce mixing requirements. Enzyme additives are also used to obtain a whiter, softer and less staling crumb. Both amylases and proteases from fungal sources are used for bread and roll production. These fungal enzymes are active during fermentation and at early stages of baking. However, these fungal enzymes are inactivated at about 65.degree. C. during baking. The bacterial amylase from B. subtilis is used to slow down firming of bread. However, the enzyme is heat stable and partially survives the baking process. The continued activity of the enzyme produces gumminess in the bread.
U.S. Pat. No. 4,299,848 describes a method whose end result is to inhibit bread firming and improve keeping qualities of bread and other bakery products. The method is based on treating a natural enzyme which is a mixture of a protease and amnylase enzymes to inactivate the protease. Various inactivation procedures are described to accomplish this end result. Fungal enzymes for baking can be stabilized against thermal denaturation by mixing the enzyme in a concentrated aqueous solution of mono- and disaccharides (U.S. Pat. No. 4,320,151).
Bacterial protease has a higher inactivation temperature (from about 82.degree. C. to about 88.degree. C.). Thus, when added to the dough, some bacterial protease enzymes survive the baking temperature and continue to act on the bread crumb after baking. Continued enzyme activity often produces undesirable gumminess in the crumb when eaten.
Ethanol is a by-product of fermentation in yeast-raised bakery products. During fermentation, the dough increases in softness, elasticity and extensibility as a result of the combined actions of water, enzymes, ethanol, organic acids and other ingredients in the recipe. As much as 2% ethanol is produced in a standard four hour fermentation. Excessive quantities of alcohol retard gas production and produce less desirable bread.